This invention relates to a roll-off hoist apparatus and method for loading and/or unloading a container onto a vehicle such as a truck used to transport the container. More particularly, the present invention relates to an apparatus to slide a unitary hoist frame along a chassis frame to jut and descend from the rear of the vehicle substantially to ground level while a forward portion of the hoist frame is swung about a pivot above the vehicle frame on piston and cylinder assemblies when loading the container onto the vehicle and when dumping material from the container; the piston and cylinder assemblies are operated to only swing the hoist frame about the pivot.
It is present-day practice to accumulate a load of waste or refuse material in a transportable container while supported on the ground by skids or rollers forming part of an understructure. The container is a large weldment with reinforced walls and usually referred to as a roll-off container. The storage capacity of the container is at least 15 cubic yards but usually not in excess of 65 cubic yards. Most containers have a capacity of 30 to 40 cubic yards. The weight of the container is relatively large even when empty. At least about 80% of the containers in use today have a standard understructure to engage with a hoist for loading and unloading the container onto a vehicle. The understructure includes spaced-apart and parallel rails projecting from the container bottom along the length thereof and wheels or skids at the four corners of the container bottom. Between these rails or outside of these rails are recessed longitudinal rails to slide along rails of a roll-off hoist during loading and unloading of the container. Some hoists will only accommodate containers where the outside rails of the understructure rail protrude downwardly below recessed rails. Most hoists will accommodate a roll-off container with either rail configuration. The hoist has parallel rails which can engage with the recessed rails in the understructure of the container and a series of rollers at spaced locations along the rails on the hoist can engage with the downwardly-protruding rails of the understructure of the container.
To load a roll-off container onto the vehicle, the vehicle is backed into a position squarely confronting the forward end of the container so that the rails of the container align with the rails on the hoist. The hoist is then swung about a pivot at the rear of the vehicle by operation of piston and cylinder assemblies connected between the vehicle and opposite forward sides of the hoist. The pivot is fixedly positioned on a rear frame portion of the vehicle to form a horizontal axis about which the hoist swings. Some hoists are constructed so that a portion of the hoist protrudes from the rear portion of the vehicle a sufficient distance so that upon swinging of the hoist, the rear portion of the hoist moves downwardly toward the ground until a ground roller on the end of the hoist frame touches the ground. Other hoists are constructed with a relatively short protruding aft portion at the rear of the vehicle whereby the container must be lifted several feet until the understructure of the container engages with the rails of the hoist. The free end of a cable of a powerful winch on the hoist is drawn out so that a hook on the end portion can be connected to a hook on the container. The container is then advanced by the winch along a hoist until the center of gravity of the container is forward of the rear pivot, whereupon the hoist is swung downwardly onto the frame of the vehicle. The container is then pulled forwardly against front stops on the hoist.
When setting off a container or dumping material from the container, the hoist must be swung about the rear pivot to elevate the forward end of the container high above the vehicle. When dumping material from the container, the doors are opened before the container is elevated so that the material can slide out of the opening at the rear of the container when it is elevated. Sometimes a push-out blade is incorporated in the container to facilitate removal of material therefrom. When it is intended to set off a container from the vehicle, after the container is swung with the hoist about the rear pivot, the winch is operated to feed out the cable and permit the container to slide along the hoist until the rear portion of the container engages the ground. Thereafter, the vehicle is slowly advanced while the forward end of the container slides along the rails of the hoist and into contact with the ground.
Another design of a hoist embodies a so-called stinger tail section. The tail section which is an independent weldment has square tubes forming spaced-apart rails that can fit inside other tubes forming rails on the hoist that terminate at the rear portion of the hoist frame. A piston and cylinder assembly is used to extend the tail section when the hoist frame is swung about the pivot so that the tail section spans the gap between the hoist frame and the ground. After a container is moved onto the hoist frame, the tail section is retracted by the piston and cylinder assembly. The roll-off container is wholly supported by the frame of the hoist. In this way, the overhung portion of the hoist can be minimized. This hoist design suffers from the acute disadvantages that the separate tail section lacks structural integrity to withstand the loads and rigorous pounding during loading and unloading of containers. The tail section deteriorates rapidly at the junction between the tail section and the hoist frame because the rails of the container's understructure upset the metal of the frame each time the container rails drop onto the rails of the extendible tail section. Moreover, the piston and cylinder assembly used to extend and retract the tail section cannot be protected from damage caused by a derailed container during a loading or unloading operation.
The present invention seeks to overcome the shortcomings and disadvantages of known roll-off hoist assemblies while at the same time substantially reduce the tremendous amount of motion and time lost when lifting or setting off a container. Known hoist designs can only swing about their pivoted rear connection so that the rear portion of the hoist rails can be lowered. The forward end of the hoist is usually swung about 17 or more feet above ground level. When a filled container is to be replaced by an empty container at a particular site, the operator must first unload an empty container from the vehicle; reposition the vehicle to load the filled container onto the vehicle; unload the loaded container from the vehicle at a closely-spaced site; reload and transport the empty container to the particular site where it is to receive material; and then reload the filled container for transportation by the vehicle. Because of the relatively large size of the container and the tremendous weight, e.g., 30 tons, that must be handled, the container loading and unloading operations are very time consuming but must be carried out in a slow and careful manner.
A further aspect of the present invention seeks to alleviate the need to elevate the forward end of the hoist frame about the pivot at the rear portion of the vehicle to such an extent that it is normally impossible to load a container onto a vehicle within a building having a restricted ceiling height.